[egberts1]

rsync would be the fastest of the lot, plus it does file permissions as well.

[acdha]

sftp is often faster since it starts copying immediately and hides latency more effectively and both sftp and scp copy permissions if you ask them to:

    -p      Preserves modification times, access times, and modes from the
            original files transferred.

[suifbwish]

rsync accepts pipes which means you can run end to end compression and decompression automatically during the transfer. Processes can also be parallelized. Most of the time when I see someone claiming rsync does not suit their purpose it ends up being that they aren’t confident in using it safely. Most of the time I never use anything else except the -av flag

[remram]

Wouldn't `rsync --ignore-existing` have similar latency from sftp then? It will be slower than rsync without the option, but not slower than sftp.